Several series of projects are planned in a continuing investigation of two neural peptides, Substance P, and neurotensin recently isolated from bovine hypothalami. The structure of Substance P has already been determined and synthetic material is available; but only a tentative structure for neurotensin has been determined. It is proposed to isolate a sufficient quantity of neurotensin by procedures already developed, establish its amino acid sequence by a combination of Edman degradation with selective enzymatic cleavages, and to prepare synthetic material by the Merrified solid-phase procedure. Efforts will be made to sensitize the radioimmunoassay for Substance P and to develop one for neurotensin. These antibody assays will be used to study the distribution of Substance P and neurotensin in different tissues and body fluids e.g. blood and cerbrospinal fluid, to measure any changes in the concentration of these peptides due to different physiological manipulations in animals or disease states in man, and to study their biosynthesis.